Caste formation in the polyembryonic wasp Copidosoma floridanum (Hymenoptera: Encyrtidae): In vivo and in vitro analysis

  1. Grbic, M. 2
  2. Rivers, D. 1
  3. Strand, M.R.
  1. 1 Loyola University Maryland
    info

    Loyola University Maryland

    Baltimore, Estados Unidos

    ROR https://ror.org/01by1wp65

  2. 2 University of Wisconsin–Madison
    info

    University of Wisconsin–Madison

    Madison, Estados Unidos

    ROR https://ror.org/01y2jtd41

Revista:
Journal of Insect Physiology

ISSN: 0022-1910

Año de publicación: 1997

Volumen: 43

Número: 6

Páginas: 553-565

Tipo: Artículo

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DOI: 10.1016/S0022-1910(97)00004-8 SCOPUS: 2-s2.0-0031171150 GOOGLE SCHOLAR

Otras publicaciones en: Journal of Insect Physiology

Resumen

The polyembryonic wasp Copidosoma floridanum produces two morphologically distinct types of larvae in its host Trichoplusia ni. Reproductive larvae consume the host, pupate, and form adult wasps, whereas precocious larvae manipulate the sex ratios of the reproductive caste and defend the brood against interspecific competitors. Previous study indicated that morphogenesis of the reproductive caste was associated with a 9-day competency period, and that ecdysteroids of host origin were required for completion of embryogenesis. Here we investigated whether factors associated with the host environment mediate morphogenesis of precocious larvae and caste determination. Embryogenesis of precocious larvae was found to be synchronized with specific stages of the host first-fourth instars. However, development of precocious larvae did not depend on environmental factors specifically associated with these host stages. Elevation of the host juvenoid titer using the analogue methoprene induced T. ni to undergo a supernumerary sixth instar, but did not alter the proportion of wasp embryos that developed into precocious and reproductive larvae. In contrast, embryos competent to initiate morphogenesis developed into precocious larvae when transplanted into novel host stages such as pupae. Development of precocious larvae was arrested by ablation of the host's source of ecdysteroids, but could be rescued dose-dependently by injection of 20-hydroxyecdysone. In vitro rearing studies confirmed that completion of embryogenesis of the precocious caste required an exogenous pulse of 20-hydroxyecdysone. Combined with previous studies, our results indicate that embryos forming precocious and reproductive larvae acquire the competence to undergo morphogenesis at different times. However, we find no evidence to suggest that caste determination is mediated by environmental factors associated with a specific stage of the host.